Yauch, 47, had helped found the pioneering trio back in 1979. He and his bandmates transformed from hardcore musicians to rappers in the '80s with the help of mentor Russell Simmons, and in the '90s, they helped along the careers of another decade of bands.

Yauch's bandmate Adam Horovitz, known to fans as Ad-Rock, shared the group's first reaction to the MC's death on their blog Sunday night, tersely describing his state of mind with a pair of expletives.

"I wanna say thank you to all our friends and family (which are kinda one in the same) for all the love and support. I’m glad to know that all the love that Yauch has put out into the world is coming right back at him. Thank you," he added.

Remembering Beastie Boy Adam Yauch

Madonna, for whom the Beasties opened on her 1985 "Like a Virgin" tour, shared her condolences on her Facebook page.

"The Beastie Boys were one of a kind! And so was Adam!" the pop queen wrote. "I'm very sad to hear about Adam's passing. God bless him and his family."

Beastie Boys' cohorts Luscious Jackson, one of the biggest bands signed to the Beasties' record label Grand Royal, offered their condolences, too: "To our brother in friendship and music Adam Yauch we will miss you deeply. Peace."

Heavyweight rappers like Common joined the tweet tribute along with indie MCs like Atmosphere and once-upon-a-time hitmaker MC Hammer.

And former Nirvana bassist Krist Novoselic noted Yauch's political activism, particularly his work organizing the Tibetan Freedom Concerts.

"Thank you for Sabotage bass riff and many other great grooves. Adam also worked for justice and peace consciousness," he noted.

And will.i.am of the Black Eyed Peas tweeted in contemplative tribute, "1 of my favorite hiphop groups...hiphop raised a lot of us & now we have to wake up because are hero's are dying too young."